POS0971 A COMPARISON OF MYOSITIS AUTOANTIBODY AND CLINICAL CHARACTERISTICS AMONG RACIAL GROUPS IN ASIA AND AUSTRALASIA – A COLLABORATIVE MULTICENTRE EFFORT BY THE APLAR MYOSITIS SIG
Authors: J. He, A. Low, M. Kuwana, L. Gupta, J. Raja, W. Fong, S. Wangkaew, H. So, T. Gono, V. Limaye
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Idiopathic inflammatory myopathies (IIM) are a group of systemic autoimmune conditions with predominant skeletal muscle involvement. Major subsets of disease recognised by the EULAR/ACR Classification Criteria include dermatomyositis (DM), amyotrophic dermatomyositis (ADM), inclusion body myositis (IBM) and polymyositis (PM) and immune mediated necrotising myositis (IMNM). Myositis-specific antibodies (MSA) more so than myositis-associated antibodies (MAA) are associated with distinct clinical phenotypes of disease and can aid in predicting the risk for extra-muscular manifestations, such as interstitial lung disease (ILD). Racial differences in autoantibody profile and clinical phenotypes have been described, though pooled intergroup comparisons are limited. <h3>Objectives</h3> We characterised the autoantibody profiles in IIM patients of different racial groups and identified relationships with IIM subsets and select extra-muscular manifestations. <h3>Methods</h3> Pooled data for adult IIM patients who had been tested for MSA and MAA was analysed. IIM subtypes were diagnosed by histology and/or EULAR/ACR criteria. Demographic, autoantibodies, clinical data, and mortality data, where available, was collected and analysed retrospectively in STATA. MSA includes autoantibodies directed against Jo1, PL-7, PL-12, EJ, OJ, Mi-2, SRP, NXP-2, TIF1-gamma, MDA5 and anti-HMGCR. MAA include autoantibodies against PM-Scl, Ku, U1RNP, and Ro52. Using multivariate logistic regression, we analysed the relationship of racial groups and autoantibodies, with (i) IIM subtypes, (ii) ILD and(iii) mortality. <h3>Results</h3> 787 (Australia (n=243), India (n=241), Japan (n=134), Malaysia (n=99), Singapore (n=51), Thailand (n= 19)) patients with IIM were analysed; 543 (67%) patients were female. The median age of diagnosis was 52 years (IQR 39, 64) with the following racial distribution: 26.7% identified as Caucasian, 37.2% East and Southeast Asian (SEA), 33.4% South Asian, and 3% other. The most frequent disease subsets were DM (n = 259) and PM/ IMNM (n = 264). MSA or MAA were detected in 351/787 patients (44.6%); of these 54.7% (192/351) were positive for MSA, 33.9% (119/351) were positive for MAA, and 11.4% were positive for both (40/351). DM was most frequently diagnosed in the East and SEA and South Asian racial groups. Controlling for demographics and autoantibodies, IIM patients of East and SEA descent were five times more likely to be diagnosed with DM (OR 5.52, 95% CI 3.19, 9.56) compared with Caucasians; South Asians were nine times more likely to be diagnosed with DM (OR 8.89, 95% CI 4.83, 16.36). Conversely in PM/IMNM, East and SEA (OR 0.20, 95% CI 0.12, 0.33) and South Asian (OR 0.34, 95% CI 0.20, 0.58) groups were much less likely to be diagnosed compared with Caucasians. Specific MSA and MAA were infrequently associated with racial groups. However, anti-SRP antibodies were 3 times more likely to be detected in the East and SEA groups (OR 2.84, 95% OR 1.04, 7.74) compared with Caucasians. Patients with anti-HMGCR antibodies were four times more likely to be diagnosed with PM and IMNM (OR 4.24, 95% CI 2.16, 8.33). MSA (OR 6.66, 95% CI 4.25, 10.43) and MAA (OR 3.06, 95% CI 1.76, 5.35) were more likely to be detected in patients with ILD; no gender difference was evident. Compared with Caucasians, East and SEA (OR 5.14, 95% CI 2.59, 10.21) patients were up to 10 times more likely to be diagnosed with ILD. Controlling for racial groups, age and gender, IIM patients with ILD had significantly higher odds of mortality (OR 1.84, 95% CI, 1.02, 3.32), though the odds were significantly lower in the South Asian racial group (OR 0.37, 95% CI 0.14, 0.92) compared with Caucasians. <h3>Conclusion</h3> Our study is the first of its kind to demonstrate an association between racial groups, clinical profiles, autoantibodies, and the subtypes of IIM. There is heterogeneity in MSA and MAA positivity among racial groups. Importantly, we show that race appears to have a possible role in the predilection for IIM subtypes and ILD. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.